384 POISONS, CONTAGION^, MIASMS. 



substances would very quickly lead td the most 

 satisfactory conclusions regarding the cause of their 

 poisonous effects. 



There is a peculiar class of substances, which are 

 generated during certain processes of decomposition, 

 and which act upon the animal economy as deadly 

 poisons, not on account of their power of entering 

 into combination with it, or by reason of their con- 

 taining a poisonous material, but solely by virtue of 

 their peculiar condition. 



In order to attain a clear conception of the mode 

 of action of these bodies, it is necessary to call to 

 mind the cause on which w^e have shown the phe- 

 nomena of fermentation, decay, and putrefaction to 

 depend. 



This cause may be expressed by the following 

 law, long since proposed by La Place and Berthollet, 

 although its truth with respect to chemical phenom- 

 ena has only lately been proved. " A molecule set 

 in motion by any power can impart its own fnotion to 

 another molecule with which it may be in co?itact,^^ 



This is a law of dynamics, the operation of which 

 is manifest in all cases, in which the resistance 

 {force, affinity, or cohesion) opposed to the motion is 

 not sufficient to overcome it. 



We have seen that ferment or yeast is a body in 

 the state of decomposition, the atoms of which, con- 

 sequently, are in a state of motion or transposition. 

 Yeast placed in contact with sugar communicates to 

 the elements of that compound the same state, in 

 consequence of which, the constituents of the sugar 

 arrange themselves into new and simpler forms, ^ 

 namely, into alcohol and carbonic acid. In these ^ 

 new compounds the elements are united together by 

 stronger affinities than they were in the sugar, and 

 therefore under the conditions in which they werei^ 

 produced further decomposition is arrested. 



We know, also, that the elements of sugar assume 

 totally different arrangements, when the substances 

 which excite their transposition are in a different 



